Impact of Pesticides

Integrated Pest Management, or IPM, is the careful and considered use of all of the options for pest management available to a grower. The focus of IPM is to use the management practises that present the lowest "risk" first, such as the exclusion of pests, sanitation methods, or the use of biological controls, while reserving the highest "risk" methods, such as broad-spectrum pesticides, for only those situations where there is no other option, such as when all of the many lower risk options have been exhausted or have ceased to be viable.

Many pesticides (insecticides, fungicides and herbicides) are toxic to beneficial organisms, including insect pollinators. This is because beneficial organisms are generally more susceptible to chemicals than the target pest species.

Many factors influence the toxicity of pesticides to beneficial insects and mites, and much care is needed when integrating the use of chemicals and beneficial organisms in IPM programmes. The effect of pesticides can also be modified by application practices and environmental conditions, so, even though a chemical may generally be regarded as ‘safe’, how and when it is applied and the conditions under which it is applied may make it less safe to beneficial organisms.

Besides the contact action of a pesticide resulting from direct spray contact, the ongoing action of pesticide residues may be harmful to beneficial organisms. The residues of many insecticides can kill beneficial insects and mites after very short exposures on the leaf or soil surface. Even when the killing power of a chemical declines as the residues disappears, sub-lethal effects, e.g., reduced reproduction, disrupted prey searching and capturing behaviour can also impact on the action of beneficial organisms.

Chemicals that are not normally applied to control insects, such as fungicides, can also have a negative effect on beneficial insects and mites. Therefore, it is important to consider all pesticides that will likely be used on a crop before beneficial organisms are introduced, and select only those that are known to be less disruptive.

‘The Good Bug Book’ Second Edition (2002), Editor Richard Llewellyn, provides a list of commonly-used chemicals and their likely toxic effects on beneficial insects and mites, and the period or waiting time which should be allowed to pass following a pesticide application before introducing beneficial insects and mites into a crop.

Refer to the label on pesticide containers for specific information about the safety of that product to beneficial insects and mites.

Guiding principles for integrating the use of pesticides and beneficial insects and mites

• If you are intending to use beneficial insects in your crop, select and use only those products, including fungicides, which are known to have few or no effects on beneficial insects.
• Apply pesticides only when monitoring or crop inspection show pest numbers are approaching damaging or recognised threshold levels.
• Observe strictly any waiting periods that are recommended when releasing beneficial insects after a pesticide application.
• Be sure your application equipment is correctly calibrated and that spray mixtures are made up accurately. Over dosing, even with some so-called ‘safe’ pesticides can be harmful to beneficial insects.
• Use the lowest effective rate recommended on the pesticide label.
• Apply pesticides at a time or in a manner that is least disruptive to beneficial insects. For example, apply a pesticide when beneficial insects are least active and direct the spray to treat only the most pest-infested parts of the plant.
• If in doubt about the safety of any pesticide to beneficial insects contact BioForce Ltd, office@bioforce.net.nz .